Automated burn-in system

ABSTRACT

An improved burn-in board cartridge for use in burn-in and testing of IC packages in an automated burn-in and test system is disclosed. The cartridge includes printed circuit cards mounted on a single or both side faces of the cartridge, thereby permitting IC packages to be mounted on either or both sides of the cartridge. The cartridge includes a sturdy frame holding in place the printed circuit cards and providing strength to reduce damage to the circuit cards. Attached to the frame are rails which are used to position the cartridge in various apparatus such as burn-in chambers. Cooling tubes and electrical components can be placed inside the two-sided cartridge, between the printed circuit cards. The burn-in chamber is divided into zones with each zone having a number of slots into which a burn-in board is placed. The chamber includes rotating air diverters positioned at each end of a zone which are capable of channeling the heated air within the chamber around any one zone. Each zone has an access door to permit loading and unloading of burn-in boards from any zone. An automated handler is provided to automatically insert and remove the burn-in board and cartridge from various units in the system. The handler includes a generally T-shaped member inserted into apertures on the burn-in board by rotating the handler with a cam lever and a first cam follower. A plurality of handlers may be used to grasp and insert a number of burn-in boards sequentially, using a second cam lever and cam follower.

RELATED APPLICATION

This application is a continuation-in-part of U.S. Ser. No. 057,255,filed June 1, 1987, entitled "Automated Burn-In System."

BACKGROUND OF THE INVENTION

The present application relates generally to the field of automatedapparatus for handling electronic circuit components, and, moreparticularly, to automated apparatus for use in the art of burning-inand testing circuit components prior to their distribution and use.Still more particularly, the present invention is directed to anautomated system wherein electronic integrated circuit (IC) packages areplaced in the burn-in system in their storage containers, automaticallyunloaded from their containers and inserted into sockets on printedcircuit (PC) boards, subjected to burn-in and, in some cases, testing inan environmentally controlled chamber; automatically removed from the PCboards, and loaded into storage devices which indicate how the IC'sperformed during the burn-in and testing. The entire process, from theinitial placement of the IC's into the system to the removal of thetested and graded IC's from the system, is completely automated andtherefore capable of "hands-off" operation.

According to present practices, IC packages are mass-produced andinstalled in electronic circuits within highly sophisticated, complexand costly equipment. As with many mass-produced products, IC packagesare prone to failure, in many cases at the beginning of operation. Thecomplexity of the equipment within which such packages are installedmakes post-installation failures highly undesirable. For example, whenequipment reaches the final inspection stage of production, beforefailures are detected, the high level skills required for testing andrepair add a significant cost to production expenses. Even moresignificantly, when the product has been installed in the field and aservice technician must make warranty repairs, the costs therebyincurred can have a significant effect on profitability. As a result,manufacturers of electronic equipment are demanding ever greater qualityand dependability in commercial grade IC packages.

Quality and dependability are enhanced substantially by detection ofthose IC packages likely to fail in the first few hours of operation,prior to installation of the packages in electronic equipment. One ofthe methods for exposing flawed IC packages is referred to as "burn-in."According to burn-in techniques, IC packages are stressed within theirphysical and electrical limits prior to installation, whereby thosepackages likely to become early failures in completed equipment can bediscovered.

Burn-in involves placing a large number of IC packages on one or moreprinted circuit boards ("burn-in boards"); placing the burn-in boardswith the packages mounted thereon in a chamber whose environment,particularly temperature, is controllable; applying direct current (dc)biases to each package on each board in such a manner as to forward andreverse bias as many of the package's junctions as possible, and/oractively clocking each package to its maximum rated conditions, suchapplication of dc biases and clock signals being accomplishedsubstantially simultaneously to each package; removing the burn-inboards from the chamber after the IC packages have been subjected to theenvironmental condition of the chamber and the biases and clock signalsfor a designated period of time; and removing the IC packages from theburn-in boards.

The burn-in process may encompass one of five general combinations ofevents. The simplest form of burn-in exposes the devices under test to aspecific temperature without supplying power or clocking signals to thedevices. In a second form, the devices are exposed to a particulartemperature and supplied with power but not with clocking signals. In athird form, the devices are raised to a particular temperature and areexercised by the addition of both power and clocking signals, but noeffort is made to monitor or evaluate performance. This third isprobably the most popular form of burn-in at the present time. In afourth form, which is gaining popularity at present, the devices arepowered and clocked at a particular temperature, and the burn-in boardinput signals are monitored to insure that a short circuit or an opencircuit at one device does not defeat the exercising of other devices.Finally, a fifth form of burn-in, which is popular especially for memorydevices, involves monitoring and functional testing of devices that arepowered and clocked at a particular temperature by monitoring outputsignals received from the memory devices. As used herein, the phrase"burn-in" or "burn-in process," unless otherwise specified, refers toany one of the five forms of burn-in described above.

A second method for improving quality control of the IC packagesubsequent to burn-in is to verify that the IC package functionsaccording to its minimum rated specifications. Typically, each ICpackage is tested across a broad range of parameters and graded inquality according to its performance. Thereafter, the IC packages may besorted into groups according to the predetermined performance grades.

The IC packages can be electrically tested either within or outside theburn-in chamber, depending on the sophistication of the particularchamber, by applying a room temperature test of critical dc parameters;for example, input currents and thresholds, output voltages andcurrents, and, in the case of digital components, by making a functionaltest to verify truth table performance. In this way, the packages thatfail during burn-in are detected and segregated from those that do notfail. Because the packages that do not fail during the burn-in processhave withstood substantial stress, such IC packages possess a highdegree of dependability and can be installed in highly complex equipmentwith reasonable confidence that such IC packages will not failprematurely.

The burn-in and testing processes, however, although successful inreducing the expense of troubleshooting failed electronic equipment, arenot themselves without expense. Substantial capital expenditures arenecessary to purchase or construct burn-in chambers, burn-in boards, andtest equipment. Personnel must be employed and trained to operate theequipment and to monitor the time-consuming processes. In some casesentire businesses have been built around performance of the burn-in andtesting processes. Use of the processes and, consequently, the successof a business that provides such services, is dependent upon the costeffectiveness of burning-in and testing the IC package vis-a-vis notburning-in or testing the IC packages but instead replacing those ICpackages that fail after installation and use in the field.

One means for improving the cost effectiveness of the burn-in process isa reduction in labor cost. There is labor cost associated with almostall steps in the burn-in process. Consequently, efforts have beenundertaken to automate certain stages of the process such as the loadingof IC packages into burn-in board sockets and unloading and sorting thesame (for example, see the commonly invented and assigned U.S. Pat. No.4,567,652, entitled "Burn-In Board Loader", and U.S. Pat. No. 4,584,764,entitled "Burn-In Board Unloader and Package Sorter"). The savings inlabor cost resulting from automating certain stages of the burn-inprocess can be substantial.

Increasing the cost effectiveness of the burn-in and testing processescan also be done by increasing the throughput of the IC packages. Sincethe burn-in process takes a great deal of time (from 6 to 160 hours), itis particularly advantageous to increase the number of IC packages whichcan be placed in the burn-in chambers. Another way to increase the costeffectiveness of the burn-in and testing process is to utilize equipmentwhich is less subject to deterioration so that repair and replacementcosts may be kept to a minimum. In addition, the reliability of theburn-in and testing process is improved when equipment is less prone togive inaccurate results due to deterioration.

A savings in the cost of labor is not the sole justification forautomating the various stages of the burn-in board process. Increasedreliability arises from the elimination of human error and the reductionof contamination when automated "hands-off" operation is present.

In an effort to realize the full benefits of automation, the focus inelectronic factories has turned to automating entire processes, insteadof merely providing islands of automation. Problems immediately arise,however, in how to integrate smoothly all components in a process. Thisproblem is intensified in the burn-in process primarily due to theuniqueness of the process. Unlike the normal process of loading ICpackages onto PC boards, the burn-in system utilizes a burn-in boardwith a uniform arrangement of sockets across the entire board; whereas atypical PC board, not designed for burn-in use is characterized by arandom arrangement of components positioned across a board designed fora particular application.

A burn-in process, unlike the normal process of loading IC packages ontoPC boards, requires that the IC packages be unloaded from the burn-inboard after the components have been subjected to burn-in and testing.This creates a myriad of difficulties such as unloading the IC packageswithout damaging them or the burn-in board; identifying which ICpackages passed and failed the burn-in and testing process; categorizingthose IC packages according to performance; precisely identifyingburn-in board and socket locations; and identifying what type of ICpackages are being tested presently so that the IC packages may behandled properly. In addition, since the sockets in the burn-in boardare subject to fatigue from re-use, defective sockets must be detectedon each board, and, furthermore, must not be used in subsequentcomponent testing until repaired.

The great length of time associated with the burn-in and testing process(6 to 160 hours) requires that the burn-in chambers be fully utilized tomaximize through-put in the process. To maximize through-put, theprocess should not operate in a sequential step-by-step manner with eachburn-in board since doing so would result in underutilization of theburn-in chamber by leaving the chamber unoccupied in whole or in partfor significant periods of time. Maximum utilization of the chamber thuscreates further difficulties in overall integration of the automatedburn-in system. This problem is intensified by the requirement that allburn-in boards be loaded into or removed from a single burn-in chamberat the same time since the burn-in boards must be cooled beforeelectrical signals can be removed; once loaded, all boards must remainin the chamber until the burn-in process is completed.

Currently, burn-in boards typically have sockets mounted to one side.Due to the size of the burn-in board, the board warps easily, andfitting the board into the burn-in chambers thus becomes a problem. Inaddition, board warpage results in deterioration of the burn-in boardcircuitry. Deterioration of the circuitry is also caused by theinsertion and removal of IC packages from the board due to the flexingwhich occurs to the board during those procedures. Conventional burn-inboards are, additionally, easily damaged and often have chipped-offcorners. The trend toward automation will only intensify the aboveproblems.

As a consequence of the problems discussed above and other problems, theindustry associated with the burn-in process to date has not achieved anautomated, "hands-off" operation.

SUMMARY OF THE INVENTION

Accordingly, there is provided a system for entirely automating theprocess of burning-in and testing integrated circuit (IC) packages. TheIC's in their storage containers are placed in the system by anoperator. The containers are grasped and identified by a handler, whichfunctions to remove the IC packages from the container. In thealternative, individual IC packages can be introduced into the system.The IC packages are placed in a tester which examines each package formechanical and electrical defects. Defective IC packages are discardedfrom the system and the remaining packages are loaded onto a burn-inboard by a loading means. The burn-in board cartridge is preferably aone- or two-sided burn-in board but alternatively may be any circuitboard capable of supporting a plurality of sockets for receiving ICpackages, or any module frame capable of supporting a plurality ofburn-in boards.

The loading apparatus may include a mechanism to sense whether the ICpackage has been inserted. If a socket refuses to accept an IC packageafter a predetermined number of attempts, then the socket is treated asdefective and consequently skipped.

After the burn-in cartridge has been loaded, it is conveyed by a shuttleapparatus to a loaded cartridge tester where the burn-in board issupplied with power. The IC packages are checked at this time to see ifany are overheating; if any of the packages are too hot, indicating"short" circuits, the IC package is removed to avoid damaging theburn-in board. If an IC package fails to warm at all, indicating an"open" circuit, the cartridge tester assumes that it is defective andremoves it from the cartridge. In both cases, a new IC package is theninserted in the empty socket. If the new IC package also is operating atan incorrect temperature the socket is assumed to be defective. The newIC package is then removed and the location of the defective socket isnoted in a central computer.

From the loaded cartridge tester the cartridge is transferred via theshuttle apparatus to a burn-in chamber where the IC packages arestressed within their physical and electrical limits, and, if theprocess includes functional testing, the performance of each package isnoted in the central computer. From the burn-in chamber the cartridge istransported to an unloading/sorting apparatus where IC packages areunloaded from the cartridge and directed to a serial IC tester. The ICpackages may be sorted at either or both the unloader/sorter and serialIC tester according to performance and placed in containers.

The automated burn-in system may further include an empty cartridgetester for the purpose of testing the sockets and circuitry on the emptycartridge for open and short circuits, and for proper capacitance andresistance. Defective sockets are detected and identified to the centralcomputer.

In addition to loaded cartridges, the shuttle apparatus can alsotransport empty cartridges and empty IC package containers. The shuttleapparatus includes a position-sensing means to permit positioning of theshuttle at a desired location, and equipment for gripping the cartridgeto enable it to move the cartridge from apparatus to apparatus.

The automated burn-in system further includes a central computer forcontrolling the flow of cartridges and IC packages between eachapparatus, for initiating operation of each apparatus, and forsupervising system operation. Individual processing units forming a partof each apparatus communicate with the central computer and control theoperation of the individual apparatus.

The burn-in board cartridge disclosed herein is capable of supportingsockets on one or both sides of the cartridge. Thus, a two-sidedcartridge includes a printed circuit ("PC") board used on both sides ofthe cartridge, thereby effectively doubling the capacity of the burn-inboard and the number of connectors which are available for signalhandling. A frame holds one or two PC boards in place on the cartridgeand serves to diminish the deterioration experienced by conventional PCboards. Damage to the board, warpage, and flexing of the board are allsignificantly reduced.

The cartridge with burn-in boards on both sides provides otheradvantages not present in conventional burn-in boards. The two-sidedburn-in board cartridge may include capacitors, resistors or digitalcircuitry in the interior of the cartridge for exercising the ICpackages during burn-in. In high speed digital logic it is highlydesirable to position the drivers as close as possible to the sockets.

The two-sided cartridge may also include a cooling means in the interiorof the cartridge. Such a cooling means reduces the exposure temperatureof electric devices in the cartridge interior, while not significantlyaffecting the ambient burn-in environment of the IC packages. Bymaintaining the cartridge interior at a cooler temperature, theeffective life of electric devices therein is prolonged.

A further advantage to the two-sided burn-in board cartridge is thatburn-in and testing of an IC package with an extremely high pin countcan be accommodated by utilizing the connectors from both sides of thecartridge. The cartridge has an improved capacity for bringing signalsinto and out of IC packages with high pin counts since the cartridge hastwice the edge-connector capacity of the traditional burn-in board.

Finally, the cartridge may be configured for use in an automatedhandling apparatus. Aligned apertures on opposing side faces of thecartridge frame combine with openings in one end thereof to enable amechanical T-shaped handling apparatus to engage the cartridge fortransport and for loading and unloading from a burn-in chamber.

The handling apparatus includes a rotational mechanism for rotating aT-shaped handle in such a manner that the handle engages the alignedaperatures. A removal mechanism is also provided to enable the handlingapparatus to connect or disconnect each burn-in board with connectors inthe burn-in chamber.

The burn-in chamber includes one or more stress chambers, each of whichis divided into a plurality of burn-in zones. Each burn-in zone iscapable of supporting burn-in and testing of a plurality of burn-incartridges substantially independent of other burn-in zones. Each zoneincludes an air diverter mechanism immediately upstream of the zonewhereby air flow may be directed around the zone to permit cooling,unloading, and reloading thereof. In this manner, IC package throughputcan be maximized.

These and various other characteristics and advantages of the presentinvention will become readily apparent to those skilled in the art uponreading the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of the preferred embodiment of the invention,reference will be made now to the accompanying drawings, wherein:

FIG. 1 illustrates schematically the preferred layout of the automatedburn-in system;

FIG. 2 shows an alternative embodiment of the automated burn-in systemwhich utilizes a shuttle traveling on an overhead rail;

FIGS. 3A and B are an operational flow chart for the incoming tubehandler;

FIGS. 4A and B are an operational flow chart for the IC tester;

FIG. 5A illustrates schematically the operation of the IC tester;

FIG. 5B is a schematic illustration of the physical test conducted on ICpackage leads to check for misalignment;

FIGS. 6A and B are an operational flow chart for the cartridge loader;

FIGS. 7A and B are an operational flow chart for the loaded cartridgetester;

FIGS. 8A-C are an operational flow chart for handling the burn-incartridge in the burn-in chamber;

FIGS. 9A-C are an operational flow chart for the cartridgeunloader/sorter;

FIGS. 10 A-I are an operational flow chart for the discharge tubehandler;

FIGS. 11A-C are an operational flow chart for the empty cartridgetester;

FIGS. 12A and B are a flow chart depicting the preferred flow of ICpackages and cartridges among individual units of the burn-in system;

FIGS. 13A-D are an operational flow chart for the shuttle apparatus;

FIGS. 14A-C are a flow chart showing priority for use of the shuttleapparatus;

FIG. 15 shows a front elevation of the preferred embodiment of theburn-in board cartridge;

FIG. 16 shows the cartridge of FIG. 15 with portions thereof cutaway todepict the internal structure of the burn-in board cartridge;

FIG. 17 shows a bottom elevation of the burn-in board cartridge depictedin FIG. 15;

FIG. 18 shows a top elevation of the burn-in board cartridge depicted inFIG. 15;

FIG. 19 shows a cross-sectional side elevation of a cartridge supportstructure with the cartridge of FIG. 15 received therein;

FIG. 20 depicts an alternative embodiment of the cartridge of FIG. 15wherein electronic components and cooling means are provided in theinterior of the burn-in board cartridge;

FIG. 21 shows an alternative embodiment of the cartridge depicted inFIG. 18 wherein an end circuit card is provided at the top end of theburn-in board cartridge;

FIG. 22 illustrates schematically the shuttle apparatus used totransport the cartridge in an automated environment;

FIG. 23 shows a side view of the single-sided cartridge;

FIG. 24 shows a front view of the burn-in chamber;

FIGS. 25A-C depict schematically the operation of the burn-in chamberair diverters;

FIG. 26 shows a side view of the burn-chamber of FIG. 24;

FIG. 27 shows a top view of the burn-in chamber of FIG. 24;

FIG. 28 shows a front view of the automatic handler;

FIG. 29 is an isometric view of the automatic handler of FIG. 28;

FIG. 30 depicts isometrically a line of automatic handlers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

"Burn-in" refers generally to any one of several techniques wherebyintegrated circuit (IC) packages are stressed within their physical andelectrical limits prior to their sale or distribution so that thosepackages likely to become early failures in completed equipment can bediscovered. The burn-in techniques include loading the IC packages intosockets on burn-in boards, placing the burn-in boards in a chamber whoseenvironment, particularly temperature, is controllable, applyingelectrical test signals to the boards while subjecting the IC packagesto the maximum temperature rating therefor (in some cases), monitoringthe test signals (in some cases), functionally testing the IC packages(in some cases), removing the burn-in boards from the chamber, andunloading the IC packages from the burn-in boards.

A typical IC package, as are referred to herein, comprises a dualin-line package ("DIP") having a body portion which is generally aparallelpiped with from four to sixty-four electrical leads of agenerally L-shaped cross-section extending out and down from theopposing sides of the body. The overall width of the DIP may be, forexample, 0.3, 0.4 or 0.6 inch. Sockets mounted on the BIC burn-in board50 include socket contacts defining slots for receiving electrical leadson DIP IC packages.

Unless specified otherwise herein, the term "IC package" may also referto a surface mounted device (a "chip carrier") including small outlineintegrated circuits (SOIC's), plastic leaded chip carriers (PLCC's),ceramic leaded chip carriers (CLCC's), leadless chip carriers (LCC's),or pin grid arrays (PGA's). The SOIC also comprises a generallyparallelpiped body portion having electrical leads extending fromopposing sides of the body. The electrical leads may have either aJ-shaped or an S-shaped ("gull wing") cross-section permitting the leadto lie on the surface of the socket instead of being inserted into slotsin the socket. The PLCC, CLCC, and LCC have bodies which are of a squareor rectangular geometry with a relatively thin cross-section, givingthese IC packages an overall wafer-shaped appearance. In the usualconstruction, the PLCC and the CLCC have multiple electrical leadspositioned flush with or bent into close proximity with the body of thepackage, while the LCC has conductive coatings applied at select areason the major body surfaces.

To accommodate surface mounted IC packages, the sockets include socketcontacts having conductive coatings on the surface of the socket. ThePGA's also have a wafer-shaped body. The leads of the PGA are usuallyuniformly spaced throughout the length and width of the bottom surfaceof the body and protrude perpendicularly therefrom. Specialzero-insertion force sockets with a separately operable closuremechanism are required to accommodate the large number and high-densityspacing of the PGA leads.

I. SYSTEM OVERVIEW

FIG. 1 shows the preferred embodiment of the automated burn-in system.The system is comprised of a number of apparatus, with each of theapparatus being responsible for a particular function in the burn-inprocess. The burn-in system includes an incoming tube hopper 110, anincoming tube handler 120, an IC tester 130, a cartridge loader 140, aloaded cartridge tester 150, a burn-in chamber 160, a cartridgeunloader/sorter 180, a serial IC tester 185, a discharge tube handler190, a pin station 265, holding bins 280, 285, an empty tube hopper 255,a discharge tube hopper 200, a shuttle apparatus 210, and a centralcontrol apparatus 900 (collectively sometimes referred to hereafter as"individual apparatus" or "unit" of the burn-in system).

The tube hopper 110 receives IC storage containers, and the tube handler120 removes the pins from the tubes and the IC packages from theirstorage containers ("tubes") and places the IC packages into the ICtester 130. The IC tester 130 runs mechanical and electrical tests onthe raw IC packages, rejecting those IC packages which fail to pass thetests. The acceptable IC packages are received at the cartridge loader140 where the IC packages are loaded on a burn-in board cartridge. Theloaded cartridge is placed in the loaded cartridge tester 150 and thecartridge is supplied with power; IC packages which have open or shortcircuits are removed from the cartridge.

From the cartridge tester 140, the loaded cartridge is transferred tothe burn-in chambers 160 where the IC packages are stressed within theirphysical and electrical limits and, if the process includes functionaltesting, the performance of each package is recorded in the host orcentral computer 900. The IC packages are subsequently unloaded bycategory, if desired, from the cartridge in the cartridge unloader 180and passed to the serial IC tester 185, which performs parametric testson each IC package. If desired, the IC packages then may be sorted intotubes according to each package's performance during the burn-in andtesting. The discharge tube handler 190 removes tubes filled with ICpackages from the cartridge unloader 180 or serial IC tester 185 andpasses the tubes to the pin station 265 to be pinned. The tubes may alsobe marked at the pin station 265 to reflect the performance of the ICpackages during burn-in and testing. Finally, the discharge tube handler190 deposits the tubes in the discharge tube hopper 200.

Referring still to FIG. 1, the automated burn-in system may furtherinclude an empty cartridge tester 240 for testing the empty cartridgefor electrical open and short circuits. If necessary, empty and loadedcartridges can be stored in a cartridge storage apparatus 230. Thecartridge is transported between apparatus by a shuttle apparatus 210disposed on a track positioned alongside of the burn-in systemapparatus. Finally, the central computer 900 serves to orchestrate theoperation of each apparatus in the system. In an alternative embodimentshown in FIG. 2, the track is located over the top of the burn-insystem.

The automated burn-in system made in accordance with the principles ofthe present invention may be constructed with one or more of theindividual apparatus comprising a dual unit in which mechanicalapparatus of the individual unit is duplicated in a side-by-side or overand under construction to increase throughput. Consequently, the systemmay be paired so that operation occurs on both halves of the dualindividual unit at the same time. It will be assumed for purposes offurther discussion that both halves of any dual unit are constructed andfunction in substantially the same manner, except as otherwise indicatedhereafter.

In normal practice, IC packages are stored in containers to protect themfrom contamination. While individual IC packages can be introduced intothe burn-in system, the preferred embodiment of the present inventioncontemplates a "tube-to-tube" process; that is, the introduction of theIC storage containers ("tubes") into the system and the receipt ofcategorized IC tubes out of the system. Such a "tube-to-tube" processeliminates the possibility that IC packages will be contaminated whenplaced into or taken out of the system. Each IC package tube used in theburn-in system has associated with it a bar code label (not shown). Thebar code label may include an orientation line which runs lengthwisewith the tube and a series of parallel lines of varying thicknessarranged generally perpendicularly of the orientation line to form aserial bar code.

Incoming Tube Hopper

Referring again to FIG. 1, the incoming tube hopper ("ITHO") 110receives tubes or containers of IC packages from a human operator andstores the same for the incoming tube handler 120.

Incoming Tube Handler

Referring still to FIG. 1, the incoming tube handler ("ITHA") 120receives tubes of IC packages from the tube hopper 110, identifies thetubes, removes the pins from the tubes and the IC packages from thetubes, and sends the IC packages to the IC tester 130.

The incoming tube handler 120 utilizes an on-board microprocessor tocontrol handler operation. FIG. 3 is a flow chart depicting thepreferred method of operation of the tube handler 120. Thus, theincoming tube handler 120 begins operation by monitoring the status oftubes in the tube hopper 110 to detect a shortage of tubes forprocessing by the burn-in system (step 310). In the event of a shortage,the tube handler 120 signals the central computer 900, and the operatoris alerted of the requirement for additional tubes as shown in step 312.

The tube handler 120 grasps tubes from the tube hopper 110 and rotatesthe tubes until the bar code orientation line is detected by a bar codereader. The bar code reader may be any conventional type, but preferablycomprises a laser scanner type reader that avoids direct contact withthe IC container. Optimally, the reader is a moving beam laser scannerthat is fixed in place while the laser beam is directed across the barcode. When the tube is properly oriented, the reader scans the serialcode on the bar code label to identify the lot numbers of the ICpackages contained in the particular tube. At step 314, this informationis compared with data received from the central computer 900 (FIG. 1)specifying the lot numbers of IC packages which are to be burned-in. Adiscrepancy between the actual lot numbers and the acceptable lotnumbers causes the tube handler to initiate an error signal which issent to the central computer 900. The unacceptable tubes then arereplaced in the incoming tube hopper 110 (step 316).

Referring still to FIG. 3, once an acceptable tube has been identified,the tube is opened at one end (step 318) and, when the IC tester 140 isready to receive IC packages, the tube handler 130 positions the tube todeliver IC packages to the IC tester 140 (step 320). The tube handler130 then continues to monitor the delivery of IC packages from the tubeinto the IC tester 140 and, after all of the IC packages have beenreceived in the tester 140, the tube handler 130 removes the empty tubefrom the tester and deposits the tube in a tube stack for pick up by theshuttle apparatus 210.

IC Tester

The IC tester ("ICTS") 130 tests IC packages for physical imperfectionsand for simple electrical defects. The IC tester 130 includes anon-board microprocessor for controlling operation of the unit. FIG. 4 isa flow chart reflecting the general operating procedure for the ICtester 130. Referring to FIG. 4, IC packages are received on infeedchannels of the tester 130 from tubes placed in position by the tubehandler 120. FIG. 5A illustrates schematically a channel track 131comprising the IC tester 130. Referring to both FIGS. 4 and 5A, thechannel track 131 is divided into an upper infeed section 301 and alower test section 303. IC packages 26 are delivered onto the upperinfeed section 301 of track 131, preferably in tubes 40. An infeed gateand an infeed sensor may be provided between the infeed section 301 andthe test section 303 to monitor the incoming IC packages. The track 131is positioned at an acute and variable angle with respect to thehorizontal to cause the IC packages 26 to pass down the track 131 inresponse to the force due to gravity. The IC tester 130 may comprise aplurality of channel tracks 131 in order to accommodate a largethroughput of IC packages. For simplicity, the discussion herein willfocus on a single track 131. Unless otherwise noted, other tracks arestructured and operate identically.

The IC tester 130 preferably includes three separate test stations. Thefirst test run by the IC tester 130 is a physical check to remove fromthe track those DIP IC packages 26 having leads which are too deformedto be loaded automatically onto the burn-in board. U.S. Pat. No.4,567,652 entitled "Burn-In Board Loader," commonly assigned, disclosessuch a test ("policing") station 199 and is herein incorporated byreference. Thus, the track 131 has a protuberance along both sides ofthe track 131 at test station A. As disclosed in U.S. Pat. No.4,567,652, the protuberance includes a widened section so as to narrowthe clearance between the sides of track 131 and an adjacent wallthrough which the leads of the IC packages 26 must pass. Any IC packages26 having electrical leads which are deformed abnormally inwardly oroutwardly with respect to the IC body portion are jammed at the narrowedclearance at station A, thereby halting the serial flow of IC packagesalong the track 131. A sensor 98 positioned below station A detects theinterruption in the flow of IC packages, alerting the on-boardmicroprocessor to the presence of a jam.

The IC packages pass through the policing station 199 one at a time. Aircylinder 174 is positioned above the track 131 and is actuated to extendthe shaft thereof and halt the flow of the IC package which is next inline to be tested. Air cylinder 174 holds the IC package until it isreleased after the preceding IC package has passed completely throughthe police station 199.

Track 131 can also be modified to accommodate IC package configurationsother than DIP's For example, where the IC packages consist of chipcarriers, the chip carrier is transported along the upper surface of thetrack 131. In addition, the track 131 may include a pair of side wallswhich extend upward alongside the upper surface of the track so as toguide the chips by contact with the side walls. The track would thusdefine a channel for slidably transporting chips through the teststations.

In the situation where pin grid arrays (PGA's) are used, the PGA can beplaced on the track described above in an inverted manner so that thebody surface lies on the track and the leads project upwardly. Theprimary test run on both the chip carriers and the PGA's are electricaltests at station C.

When the IC tester 130 is alerted to a jam condition, an ejectionmechanism 37 within the track 131 removes the jammed IC package 26 fromthe track. The ejected IC package is deposited into a mechanical rejectbin 238 where it can be collected later by an operator for furtherprocessing or disposal (step 330).

Leads which are not deformed abnormally inwardly or outwardly may stillbe unacceptable if the leads are missing or if the leads are bentlaterally with respect to the IC body portion. Referring still to FIGS.4 and 5A, the second test performed by the IC tester 130 is also aphysical check; the IC packages 26 are examined at test station B byoptical sensors to insure that the leads are present and are properlyaligned in terms of lead spread and straightness. Test station Bincludes a gate 137 to halt the flow of IC packages down the track 131so as to permit examination of individual IC packages; optical sensorspositioned adjacent to the track detect lead misalignment. Test StationB is shown in detail in FIG. 5B. The optical sensors include a pluralityof photoelectric transmitters 138 and photoelectric receivers 142 fordetecting lead misalignment. If an IC package is found to be defective,it is ejected automatically into the mechanical reject bin 238 by anejector mechanism 133 positioned within the track 131 (step 330).

Referring still to FIGS. 4 and 5A, the third test conducted by the ICtester 130 is an electrical check for open and short circuits at teststation C. Test station C includes a gate 139 to halt the flow of ICpackages down the track 131. Positioned above track 131 is air cylinder176 which includes a plurality of electrical probes 101 to contact theleads 33 of the IC package 26. Once the IC package is stopped at gate139, air cylinder 176 is actuated to extend probe 101 into contact withthe leads of the IC package. The IC package 26 positioned at the teststation C is also examined to insure that it is properly oriented. Ifthe IC package is improperly oriented, it is rotated 180° end for end.The tester 130 is programmed to conduct open circuit and short circuitchecks with the probe 101, and any IC packages found to have electricaldefects are ejected from track 131 into an electrical reject bin 308 byejector mechanism 103 (step 332).

During the three tests conducted in the IC tester 130, mechanical andelectrical defects are recorded and communicated to the central computer900, as are the number of IC packages which pass all tests. Since thecentral computer 900 already received from the handler 120 the identityof the tubes within which the IC packages were stored, it is thereforepossible to associate the number of defects with a particular tube andlot number.

Cartridge Loader

On leaving the IC tester 130, the IC packages pass to the burn-incartridge loader ("BCLD") 140, as shown in FIG. 1. The loader 140 isresponsible for placing the IC packages onto burn-in cartridges. Oneexample of such a loader is disclosed in commonly assigned U.S. Pat. No.4,567,652, granted to the present inventor, which is incorporated hereinby reference. The preferred manner of placing the IC packages on theboard may differ, however, from that disclosed in U.S. Pat. No.4,567,652. In addition, the traditional burn-in board used in U.S. Pat.No. 4,567,652 preferably is replaced by a burn-in board cartridgedescribed herein.

The function of the loader 140 is to mount IC packages in sockets onburn-in board cartridges. The cartridge loader 140 preferably includes aloader incoming buffer, a loading station, and a loader dischargebuffer. The loader incoming buffer stores empty burn-in boardcartridges. The loading station is the position at which emptycartridges are loaded with IC packages, and the loader discharge bufferreceives loaded burn-in cartridges for storage. Both the incoming andthe discharge buffers are capable of storing a plurality of cartridges.The loader 140 automatically moves the cartridge from the incomingbuffer to the loading station and from the loading station to thedischarge buffer. In addition, a mechanism is provided in the loadingstation for rotating the cartridge 180° to permit loading on a secondside of the cartridge if a two-sided cartridge, described infra indetail in section II, entitled "Burn-in Cartridge". Bar code readers arepositioned in the incoming buffer and the loading station to scan a barcode label placed on the burn-in board surface or surfaces to identifythe cartridge and the specific side face of the cartridge.

Loading of IC packages onto the cartridge proceeds automatically withprecise position placement of the packages by a loading mechanism.Associated with the loading mechanism is a sensing means for determiningwhether an IC package has been properly inserted into the sockets on theburn-in board cartridge.

The preferred manner of operation of the cartridge loader 140 is setforth in the flow chart of FIG. 6. The operation of the loader iscontrolled by a microprocessor unit programmed in accordance with theoperational flow chart. Referring now to FIGS. 1 and 6, the operation ofthe cartridge loader 140 can be broken into two portions--an auxiliaryportion 141 and the actual loading portion 143. In the auxiliary portionof loader operation, the incoming buffer is monitored for the presenceof empty cartridges at step 350. As shown in step 352, the absence of anempty cartridge causes the loader 140 to signal the central computer 900that empty cartridges are required at the loader 140. Similarly, a lackof IC packages available for loading causes the loader 140 to notify thecentral computer 900 that IC packages are not available for loading.Once a burn-in cartridge is selected for loading, the bar code readerscans the bar code label on the side face of the cartridge to identifythe burn-in cartridge. This information is compared with anidentification of the burn-in cartridges suitable for use with theparticular lot number of IC packages to be loaded (step 354). Adiscrepancy causes the loader 140 to exchange the burn-in cartridgeselected for loading.

When a suitable cartridge has been identified, a determination is madeat step 356 as to whether the particular side face of the selectedcartridge has already been loaded with IC packages; if the cartridge hasbeen loaded it is transferred to the discharge buffer and the centralcomputer 900 is so notified. If the discharge buffer lacks room for theloaded cartridge, the cartridge loader signals the central computer 900to have the shuttle pick up cartridges from the discharge buffer.

Referring still to FIGS. 1 and 6, if the selected cartridge has an emptyside face and the auxiliary portion of the loading operation iscompleted, the actual loading portion 143 of the operation can begin.The burn-in board cartridge is moved into loading position at step 358by aligning the first row of cartridge sockets with the loadingmechanism. At that time, the central computer 900 downloads a GoodSocket Map, which identifies to the loader 140 the sockets that arefunctioning properly on the particular cartridge then in use, and ICpackages are mounted in all good sockets in the pre-positioned row. Asensor detects if any IC package fails to mount properly in a socket. AnIC package that does not mount properly is removed from the socket anddropped into a holding bin, and an attempt is made to mount another ICpackage in that socket. If two consecutive IC packages fail to mount inthe same socket, the socket is considered defective and is deleted fromthe Good Socket Map.

When all of the good sockets in the row have been loaded, the cartridgeloader 140 determines whether that row is the last row of the cartridge(step 360). A finding that it is not the last row initiatesrepositioning of the cartridge so that the next row is aligned with theloading mechanism. After all rows on a side face of the cartridge havebeen loaded, the identification of the cartridge and the side face,along with a Load Map, are sent to the central computer 900. Inaddition, if a two-sided cartridge is in use, the cartridge is rotatedso that the other side face is in position for loading. The auxiliaryportion 141 of the operation then begins for the second side face of theselected cartridge with a determination of the availability of ICpackages, as described supra.

Loaded Cartridge Tester

Referring now to FIG. 1, after the cartridge is loaded, it may betransferred by the shuttle apparatus 210 to the loaded cartridge tester("LBTS") 150, if testing is desired. The loaded cartridge tester 150preferably includes an input buffer, a test station, and an outputbuffer. Loaded cartridges which are ready to be tested are placed in theinput buffer, and tested cartridges are stored in the output buffer.Both buffers are capable of storing a plurality of cartridges. Transferbetween the buffers and the test station is done automatically withinthe tester 150. Positioned in the input buffer or the test station is abar code reader which scans the bar code label on the cartridge andidentifies the cartridge and side face of the cartridge to be tested. Aheat sensitive scanner is used in the tester 150 to sense thetemperature of the IC packages during the testing process. In addition,the tester 150 preferably includes a loader means and an unloader meansfor the removal and replacement of defective IC packages and a mechanismfor rotating a two sided burn-in cartridge if such a cartridge is usedin the system. Finally, electrical test connectors are placed in thetest station to provide power to the cartridge.

The loaded cartridge tester 150 includes a microprocessor to controltester operation. The tester 150 operates generally as shown in the flowchart of FIG. 7. Referring now to FIGS. 1 and 7, the loaded cartridgetester 150 initially monitors the presence of loaded cartridges in theinput buffer at step 372; the absence of loaded cartridges is noted, anda signal reflecting the same is relayed to the central computer 900. Aburn-in cartridge is automatically moved from the input buffer to thetest station where the bar code reader scans the bar code label on oneor both side faces of the cartridge to find a side face of the cartridgethat has not been tested. If both sides of a two-sided cartridge havebeen tested, or if the side face of a single-sided cartridge has beentested, the cartridge is transferred to the output buffer, the centralcomputer 900 is notified, and a new cartridge is sought.

On finding that a side face of the cartridge has not been tested, theloaded cartridge tester 150 determines whether the proper test programfor that particular cartridge is present in the tester microprocessor(step 374); if necessary, the program is retrieved from the centralcomputer 900. The IC packages then are tested row-by-row andsimultaneously examined by the heat sensitive scanner to determinewhether any of the IC packages are overheated or underheated. Theunloader means removes IC packages not within a specified range of aparticular temperature, and the loader means places the new IC packagesin their place. If a new IC package also fails to exhibit an acceptabletemperature, the tester 150 notifies the central computer 900 that thesocket is defective. The loaded cartridge tester 150 therefore serves asa prescreening check to prevent damage to the burn-in system during theburn-in and testing that occurs in the burn-in chambers. After the lastrow of the cartridge is scanned, the loaded cartridge tester 150 rotatesthe two-sided cartridge and scans the opposite face to determine whetherboth sides have been tested. Tester operation then proceeds accordingly.

Burn-In Chambers

Referring now to FIG. 1, when prescreen testing is completed in theloaded cartridge tester 150, the cartridge is transferred to the burn-inchambers ("BICH") 160. A number of identical burn-in chambers may beprovided; each burn-in chamber includes a plurality of electrical zones,all of which operate at the same temperature. In addition, each zoneincludes a number of slots ("n") for receiving burn-in cartridges. Thenumber of slots ("n") may be, for example, four to eight slots. In thepreferred embodiment, cartridges are loaded in the burn-in chambershorizontally from the shuttle apparatus 210, which passes alongside theburn-in system apparatus (FIG. 1). Alternatively, if an overhead shuttleis used, cartridges may be received vertically through the top of theburn-in chamber (FIG. 2).

The operation of the burn-in chambers 160 is controlled by one or moremicroprocessors, programmed in accordance with the flow chart of FIG. 8.Referring now to FIGS. 1 and 8, the burn-in chamber initially examineseach of the chamber zones at step 390 to determine whether any zoneshave completed a burn-in cycle. A determination that one of the zoneshas completed the burn-in cycle leads to an inquiry as to theavailability of burn-in board cartridges requiring burn-in. Whencartridges are available, the central computer 900 downloads relevantdata, including the lot number of the IC packages, the serial number ofthe burn-in cartridge, and the burn-in plan. In addition, a check ismade at step 392 to insure that the results from the loaded cartridgetester 150 have been reported to the central computer. If any of thecartridge data is missing from the central computer 900, the operator isalerted.

The burn-in chamber 160 then determines whether there is space in achamber zone to accommodate one or more cartridges (step 394). If openslots are located in a zone, a determination is made as to whether thezone operating temperature is acceptable or, if not, whether it can beadjusted. If a zone with the proper operating temperature is located, adetermination is made as to whether the proper driver boards areavailable.

Once the burn-in cartridges are installed by the shuttle apparatus 210,the burn-in cycle (which may include testing) commences. The performanceof each IC package during the burn-in cycle is noted and reported to thecentral computer 900. Once a zone completes a burn-in cycle and the zonehas cooled, and all electrical communication with the cartridges hasceased, the chamber 160 notifies the central computer 900 that thecartridges are ready for removal.

Cartridge Unloader

After the burn-in and testing process has been completed in the burn-inchambers 160, burn-in cartridges are transferred to the cartridgeunloader-sorter ("USRT") 180. The cartridge unloader-sorter 180 includesan unloader input buffer, an unloading station, and an unloaderdischarge buffer. Cartridges are received in the unloader input bufferand then transferred to the unloading station for processing. Theunloading station has associated with it a mechanism for rotating thecartridge (if necessary), an unloading mechanism for releasing ICpackages from the sockets on the burn-in board cartridge, and a bar codereader for scanning the bar code label on each side face of thecartridge. The unloader preferably also includes means for sorting theIC packages according to performance grades in the event that the ICpackages undergo testing and consequent grading within the burn-inchamber. Commonly assigned U.S. Pat. No. 4,584,764, entitled, "AutomatedBurn-In Board Unloader and Package Sorter," incorporated herein byreference, discloses a prior art unloader-sorter apparatus.

An on-board microprocessor controls operation of the unloader-sorter 180as shown generally in the flow chart in FIG. 9. Referring now to FIGS. 1and 9, the unloader-sorter 180 begins operation (step 402) by monitoringthe presence of burn-in cartridges in the unloader input buffer. Asshown in step 404, the central computer 900 is informed of the absenceof cartridges in the input buffer. A cartridge in the input buffer ismoved automatically to the unloading station and the bar code label onone or both of the cartridge side faces is scanned by the bar codereader in an attempt to locate a side face loaded with IC packages. Ifthe cartridge has already been completely unloaded, it is transferred tothe unloader discharge buffer, and another burn-in cartridge is removedfrom the input buffer.

When a cartridge side face with IC packages is located, the appropriateunload and sort program is downloaded from the central computer 900 tothe unloader 180. Before the unloader 180 begins to unload thecartridge, it determines whether a sorting operation is to take place(step 408). In instances where no sorting is to occur, the unloadingmechanism then unloads IC packages from the cartridge row-by-row. Afterall rows are unloaded, the cartridge, if two-sided, is rotated and thebar code scanner examines the label on the other side face of thecartridge to determine whether unloading is required (step 406).

In the preferred embodiment, if a sorting operation is to take place,the unloading mechanism is instructed to unload a particular grade of ICpackage from the cartridge row presently aligned with the unloadingmechanism. The unloader 180 confirms that a storage container ("tube")is in place for receiving the particular grade of IC package and thatthe tube has room to accommodate additional IC packages. As each ICpackage of the particular grade is released and delivered to a tube, itis counted by the unloader 180 (step 410). A bar code scanner identifiesthe particular tube and the unloader/sorter communicates thisinformation, along with the lot number of the IC packages placedtherein, to the central computer 900. After all the IC packages of aparticular grade are removed from the row being unloaded, the unloaderdetermines whether all IC packages have been unloaded from that row. Ifany IC packages remain, another grade of IC packages is unloaded, andthe process is repeated until the row is completely unloaded. Once therow is unloaded, the cartridge is repositioned to the next row of ICpackages, and the row is unloaded by grade of IC packages. When all rowsare unloaded, the cartridge, if two-sided, is rotated and operationpicks up at step 406 with the scanning of the bar code label.

Discharge Tube Handler

The discharge tube handler ("THDE") 190 coordinates the flow of ICpackages in storage tubes from the unloader/sorter 180 to the dischargetube hopper 200, diverting tubes of IC packages to the serial tester 185when testing is desired, as shown in FIGS. 1, 2, and 12. The serial ICtester 185 performs parametric tests on the IC packages. A pin station265, associated with the tube handler 190, caps the full tubes beforethe tubes are placed in the discharge tube hopper 200. In addition, thepin station 265 may mark the individual IC packages according toperformance during testing. If marking is desired, the tube is emptiedonto a track similar to that used in the IC tester 130. The packages aremarked and then pass down the track into an empty tube; the tube ispinned after all IC packages have descended down the track. The tubehandler 190 can also place tubes in a pair of holding bins 280, 285which serve as temporary storage areas for full tubes passing to andfrom the serial tester 185 and to and from the pin station 265. The tubehandler 190 receives empty tubes from an empty tube hopper 255, whichstores empty tubes received from the incoming tube handler 190 by meansof an operator or the shuttle apparatus 210. Consequently, the emptytube hopper 255 is preferably positioned adjacent the discharge tubehandler 190 in a manner permitting access thereto by the shuttleapparatus 210.

The operational flow chart for the tube handler 190 is shown in FIG. 10,and a microprocessor is programmed accordingly to control dischargehandler operation. The tube handler 190 obtains empty tubes from theempty tube hopper 255 and places these tubes at the output of theunloader 180 and at the output of the serial IC tester 185 as required.The tube handler 190 monitors the level of IC packages in the tubes atthe cartridge unloader 180 (step 420). Once a tube is full of ICpackages, the handler 190 distinguishes between sorted IC packages andunsorted IC packages. Sorted IC packages are removed in tubes byperformance grade while unsorted IC packages are removed uniformly intheir tubes. When serial testing is required, the tube handler removesthe tube full of IC packages from the unloader 180 and deposits it atthe input of the serial tester 185 or at holding bins 280,285 if spaceis unavailable at the serial tester. The tubes are fed to the serialtester 185 by category when a sorting operation occurs at theunloader-sorter 180.

In situations where serial testing is unnecessary, or after serialtesting is completed, the discharge tube handler 190 places the tube atthe input of the pin station 265. Alternatively, the tube may be placedat holding bins 280,285 until space becomes available at the pinstation.

The tubes are capped at pin station 265, picked up by the tube handler190, and placed in the discharge tube hopper 200, or in holding bins280,285 until space is available in the discharge tube hopper 200. Thetube handler 190 also removes empty tubes from the input of the serialtester 185 and places them in the empty tube hopper 255 (step 422).

A bar code reader is preferably provided at the serial tester 185, pinstation 265, and holding bins 280,285 to identify the tubes and thusinsure that the tubes are transferred by the tube handler 190 in propersequence to the desired destination.

Discharge Tube Hopper

Referring now to FIG. 1, the discharge tube hopper ("DTHO") 200 issimilar to the incoming tube hopper 110. The discharge tube hopper 200may include, for example, a storage bin into which the discharge tubehandler 190 places the tubes filled with IC packages. The discharge tubehandler 190 delivers the filled tubes to the discharge tube hopper 200.The operator then removes the tubes from the tube hopper 200.

Empty Cartridge Tester

Referring still to FIG. 1, after the burn-in board cartridge is unloadedat the cartridge unloader 180, the cartridge may be delivered to theempty burn-in cartridge tester ("EBTS") 240, if empty cartridge testingis desired. The cartridge tester 240 examines the empty cartridge forelectrical open or short circuits to identify sockets that are notfunctioning properly. A Good Socket Map is generated and sent to thecentral computer 900; this socket map is used by the cartridge loader140 during the loading process so that IC packages are mounted only ingood sockets.

The empty cartridge tester 240 includes an input buffer, a test station,and a discharge buffer. The input buffer and discharge buffer serve asstorage areas for the cartridge before and after being tested. Thetester 240 utilizes an electrical test probe which is inserted into eachsocket on the cartridge. The probe resembles an IC package to the extentthat it includes a plurality of conductive leads which are inserted,like an IC package, into the socket. A BIC ("burn-in cartridge") rejectbin 249 stores burn-in cartridges that include an excessive number ofbad sockets.

The tester 240 is controlled by an on-board microprocessor, programmedin accordance with the flow chart of FIG. 11. Referring now to FIGS. 1and 11, tester 240 begins its operation at step 430 by monitoring thepresence of burn-in cartridges in the input buffer; the central computer900 is notified in the event of an absence of cartridges. Once acartridge becomes available, it is placed in the test station. The barcode label on the side face of the cartridge facing the electrical testprobe is scanned by a bar code reader to identify the cartridge and theparticular side face. The tester 240 communicates with the centralcomputer 900 to determine whether this particular cartridge should betested (step 432). A determination that the cartridge is not to betested causes the cartridge to be transferred to the discharge buffer.

If testing is to proceed on the cartridge under examination, the tester240 determines whether the side face of a single-sided cartridge, orboth side faces of a two-sided cartridge, have already been tested. Ifthe side faces of the cartridge have been tested, the cartridge istransferred to the discharge buffer, and the central computer 900 issubsequently notified.

Once the tester 240 determines that a side face of the cartridge needsto be tested, the tester 240 requests the central computer 900 todownload the test plan, and the side face of the cartridge is tested byinserting the test probe into each socket. After the test is concluded,the tester 240 determines whether the cartridge has met minimumspecification requirements by having less than a predetermined thresholdnumber of socket failures (step 434). If the side face exceeds thepredetermined threshold, the cartridge is sent to the BIC reject bin249, and the test results are reported to the central computer 900. Forthose cartridges that pass the test by meeting the minimumspecifications, a socket map designating good (or bad) sockets for thatside face is sent to the central computer 900. The cartridge, iftwo-sided, is then rotated, and the process is repeated commencing atstep 431.

Burn-In Cartridge Storage and Tube Dump

Referring again to FIG. 1, the burn-in system preferably includes aburn-in cartridge ("BIC") storage area. The BIC storage 230 is used tostore temporarily both empty and loaded cartridges which are awaitingthe next stage of processing in the burn-in system. The BIC storageinteracts primarily with the cartridge unloader 180, the empty cartridgetester 240, and the cartridge loader 140 (see FIG. 12). In addition, theBIC storage may interact with the loaded cartridge tester 150, theburn-in chamber 160, the cartridge unloader 180 and the cartridge loader140. The BIC storage may include a bar code reader for ascertaining theidentity of stored cartridges.

The automated burn-in system of the present invention may also include atube dump area 245 to receive from the incoming tube handler 120 andstore empty tubes which are not to be re-used. The tube dump 245includes a bar code reader to identify the "dumped" tubes to insure theyare not re-used accidentally. The tube dump area 245 can be located anyplace within the in-line system.

Cartridge Shuttle

The shuttle apparatus 210 transports the cartridges among the individualunits of the burn-in system as reflected in FIG. 12, positionscartridges in the individual units, and removes cartridges fromindividual units. The shuttle preferably passes alongside the systemapparatus as illustrated in FIG. 1, and therefore loads and unloadscartridges by generally horizontal motion into and out of (or onto andaway from) each apparatus. FIG. 2 depicts an alternative embodiment inwhich an overhead rail is used to transfer cartridges vertically betweenthe shuttle and the system apparatus. FIG. 12 shows schematically theflow of cartridges and IC packages among the individual units of theautomated burn-in system. The shuttle apparatus 210 includes an on-boardmicroprocessor programmed in accordance with the flow charts shown inFIGS. 13 and 14. The basic control routine, shown in FIG. 13, detectsshuttle position and plots future actions. FIG. 14 depicts a subroutinethat establishes priority for the various shuttle activities.

Referring now to FIGS. 1, 13, and 14, the shuttle apparatus 210maintains constant awareness of its location in the burn- system. If theposition is unknown, the shuttle executes a series of maneuvers, asshown in step 452, designed to identify its position. After ascertainingits location, the shuttle apparatus 210 plots its course by analyzingthe apparatus presently on-board the shuttle. The shuttle firstdetermines whether it has on-board empty burn-in cartridges, loadedburn-in cartridges, or empty tubes. If there are empty cartridgeson-board the shuttle, the shuttle determines the ultimate destination ofthe empty cartridges. Once a proper destination is found, the basiccontrol program exits to the priority subprogram of FIG. 14. If a properdestination is not identified, the central computer 900 is notified, andexecution of the basic control program continues.

If no empty cartridges are on-board, the shuttle apparatus 210 considerswhether there are loaded burn-in cartridges on-board the shuttle (step456). If loaded cartridges are on-board and their destination isidentified, execution is transferred to the priority subroutine. In theabsence of loaded cartridges or a known destination, execution of thebasic control program continues.

The shuttle apparatus 210 next determines at step 458 whether emptytubes are on-board and if so, the intended destination for the tubes. Asbefore, the presence of empty tubes and the known destination transfersexecution to the priority subprogram. In the absence of empty tubes or aknown destination, execution of the basic control program continues.

In the absence of cartridges or empty tubes on board the shuttle, theshuttle apparatus 210 determines whether any individual unit in theburn-in system requires attention (step 460). If so, execution istransferred to the priority subprogram.

In the priority subprogram of FIG. 14, the basic services provided bythe shuttle are ranked in order of priority. It should be noted thatthis priority ranking may vary from system to system and within any onesystem from time-to-time due to a variety of factors, including the timerequired to burn-in and test a particular type of IC package.

As shown at step 470, execution of the priority subprogram commenceswith a determination, by order of priority, of the individual unit thatwill be serviced first by the shuttle. Once the prioritized target isidentified, the shuttle determines whether it can perform moreefficiently by servicing a unit more proximate to the shuttle apparatus(step 472). If the shuttle has on-board the necessary equipment orspace, or if it can pick up the necessary equipment on the way to thecloser unit, the shuttle is instructed to service the closer unit.Alternatively, if a unit which is positioned between the shuttle and itsdestination needs attention and the shuttle can perform more efficientlyby servicing the intermediate unit, it is instructed to do so. Finally,if it is most efficient to service the prioritized machine, thatactivity is conducted first.

The shuttle apparatus 210 used in the horizontal loading system of FIG.1 may also include equipment for raising the shuttle to access aplurality of horizontal levels in the burn-in system.

Central Control Apparatus

Referring again to FIG. 1, the host or central computer 900 is connectedelectrically to each individual unit in the system (except the hoppers110,200, and the tube dump 245) and serves to coordinate operation ofthe various units. The connection to the shuttle apparatus 210 may be byremote control, overhead wire, through the shuttle rails, or any othersuitable means. At the beginning of a burn-in operation, the operatorenters into the central computer 900 the lot numbers of the IC packagesto be tested, the number of IC packages in the lot, the type of ICpackages in the lot, and the burn-in plan (including time, temperature,and signal information). As the burn-in of the IC packages progresses,the central computer 900 receives additional information and messagesfrom the various microprocessors in the system, such as test results andlocations of the IC packages and cartridges, and, when necessary, relaysneeded data to apparatus in the system.

II. BURN-IN CARTRIDGE

The automated burn-in system constructed in accordance with theprinciples of the present invention includes a single-sided and/or atwo-sided burn-in cartridge ("BIC") for supporting IC packages duringthe burn-in process. Referring now to FIG. 15, the BIC 50 includes agrasping end 400, a connector end 300, lateral sides 225, 226, and oneor two side faces 56. FIG. 15 shows one side face 56 of the BIC 50. Itwill be assumed for purposes of this discussion that when two-sidedBIC's are used the second side face of the cartridge is identical to thefirst; in fact, however, the two side faces of the cartridge may differin circuit design or otherwise as desired. Each side face of thetwo-sided cartridge is made up of a standard printed circuit card 30onto which sockets 38 are mounted A single- sided cartridge has only oneside face and thus uses only a single printed circuit card 30.Integrated circuit (IC) packages 26 that are to be processed in theburn-in system are inserted into the sockets 38.

This discussion focuses primarily on the two-sided cartridge. Thesingle-sided cartridge utilizes the same structure as the two-sidedcartridge except as noted herein. Referring now to FIGS. 15-18, theprinted circuit cards 30 are held in place by frames 21,22. Frames 21,22are elongated metal brackets with a generally U-shaped cross-sectionwhich extend along substantially the entire length of the lateral sides225, 226 of the cartridge 50. Preferably, the frames 21, 22 are composedof aluminum and are approximately 24 inches long and 1.5 inches wide(equivalent to the width of the cartridge). The U-shaped frames have auniform material thickness of about 0.15 inch. The cards 30 are securedto the opposed inside surfaces of the U-shaped frames by suitablefastening means such as screws, bolts, or rivets.

FIG. 16 illustrates one side face of the two-sided BIC 50 with a portionof the printed circuit card 30 removed exposing the interior of the BIC50. The back side 35 of the second printed circuit card 30 of atwo-sided cartridge is now viewable. Between the two printed circuitcards 30 or behind the single printed circuit card of the single-sidedcartridge are cross-beams 31. The cross-beams 31 are three-dimensionalrectangular structures positioned uniformly along the length of the BIC,perpendicularly to frames 21, 22. Preferably, the cross-beams arecomposed of a non-conducting plastic such as "DELRIN," made by DuPont,and are approximately 16 inches long and 1.5 inches wide (width ofcartridge), with a thickness of about 1.0 inch. In the preferredembodiment, five cross-beams 31 are utilized between the first andsecond printed circuit cards 30. One cross-beam is positioned at boththe top and bottom ends of the BIC, and the other three cross-beams arespaced equidistantly therebetween. Interior chambers 43 are defined inthe space between two adjacent cross-beams, within the interior of thetwo-sided BIC. Thus, in the preferred embodiment, the five cross-beams31 define four interior chambers 43.

Cross-beams 31 have boreholes 41 through which cooling tubes 46, 48 maybe passed for use with the two-sided cartridge. Referring to FIGS. 16and 20, boreholes 41 are preferably about 1 inch in diameter and extendthrough the cross-beams 31 in a direction generally parallel to theU-shaped frames 21, 22. While cooling tubes 46, 48 may pass through theentire interior of the two-sided BIC 50 by means of boreholes 41 in eachof the interior cross-beams 31, the preferred manner of cooling is toinsert the tubes only into an end interior chamber 43a. Consequently,cooling holes 264, 266 (FIG. 17) are provided in the bottom endcrossbeam of the two-sided cartridge for receiving tubes 46, 48 (FIG.20). Airflow through the boreholes 41 then provides cooling to the otherinterior chambers 43. In order to reduce the exposure temperature ofelectronic circuitry in the cartridge interior, and pressurize theinterior against the influx of hot gases from the chamber, nitrogen orcool ambient air may be blown in through tube 46, while the outflow ofair passes through tube 48.

The connector end 300 of the cartridge is illustrated in FIG. 17. TheBIC 50 is electrically connected to the circuitry of a burn-in chamberor other apparatus through connectors 25: These connectors 25 may be anyconventional type such as edge or pin connectors. In the preferredembodiment, rails 28, 29 are provided along the outer lateral side offrames 21, 22 for engagement within a track 49, 51 set in the burn-inchamber, or any other individual unit into which the BIC 50 is placed(see FIGS. 15 and 20).

Referring now to FIGS. 19 and 20, the apparatus into which the BIC 50 isplaced includes a cartridge support structure 61 comprising sidesupports 64, 65 and an end support 68. The side supports 64, 65 are madeof sheets of a rigid material, for example, aluminum, and extendperpendicularly from end support 68 to a distance of approximately 24inches. At the far end of each side support 64, 65 is a flange 72, 74lying in a plane perpendicular to the outer surface of each sidesupport. Extending perpendicularly along the inside surface of the sidesupports 64, 65 are tracks 49, 51 into which the rails 28, 29 of thecartridge 50 slide.

End support 68, which may be composed of the same material as sidesupports 64, 65, forms the base of the cartridge support 61, giving thecartridge support 61 a generally U-shaped cross-section. The end support68 is a two-layered structure with an outer layer 67 and an inner layer69, similar to that shown and described in commonly assigned U.S. Pat.No. 4,374,317, which is incorporated herein by reference. The flanges72, 74 of the side supports 64, 65 are secured to the outer layer 67 bysuitable fastening means; the distance between the side supports 64, 65is approximately 16.5 inches. Preferably, the outer layer 67 has agenerally rectangular slot 63 forming an opening for receiving theconnector end 300 of the BIC 50 therethrough. Slot 63 is positioned sothat its longitudinal axis is centered on a line between the two tracks49, 51. The longitudinal length of slot 63 is about 15 inches while thetransversal length is about two inches.

Inner layer 69 is placed about two inches beyond outer layer 67.Apparatus connectors 66 are mounted on the inner layer 69 and arepositioned directly beyond rectangular slot 63. Electrical connectionsextend from the back of apparatus connectors 66, through inner layer 69,to apparatus circuitry (not shown). Cooling tubes 46, 48 may also bepositioned proximate to the apparatus connectors 66 beyond slot 63.Tubes 46, 48 extend to a height of about 1 inch from inner layer 69.Nitrogen or cool ambient air can be blown through tube 46 into thecartridge with the outflow of air from the cartridge passing throughtube 48.

When the BIC 50 is placed into the cartridge support structure 61,cartridge rails 28, 29 are received within tracks 49, 51, effectivelytargeting the BIC 50 into the unit in such a manner that, when fullyinserted, cartridge connectors 25 will contact apparatus connectors 66and cooling tubes 46, 48 will be inserted into the two-sided BIC 50through cooling holes 264, 266. Inserting the BIC 50 in this manner alsoinsures that the exact location of the BIC 50 and its sockets may bepredetermined for purposes of further automated handling of the BIC orIC packages loaded thereon. A number of cartridge support structures 61may be utilized in individual units to increase the number of BICs 50that can be processed.

The BIC structured in accordance with the principles of the presentinvention may further include apparatus for automated handling of boththe one and two-sided BIC 50. Referring now to FIGS. 15 and 18, suchhandling apparatus may include apertures 8, 9, cavities 11, 12, andcarrier means such as the shuttle apparatus 210 (FIG. 1). Apertures 8, 9are provided through both of the side faces 56 near the grasping end 400of the BIC 50. The apertures 8, 9 are generally cigar-shaped, with alength of approximately two inches and a width of 0.5 inch. Rimming theapertures 8, 9 are rings of a rigid material, such as aluminum, set inthe printed circuit cards. The apertures 8, 9 are positionedapproximately 0.5 inch from the grasping end 400 of the BIC 50 withaperture 8 positioned approximately three inches from the left lateralside 225 of the BIC 50 and aperture 9 positioned approximately 3 inchesfrom the right lateral side 226 of the BIC 50.

The cavities 11, 12 form generally cigar-shaped openings in the graspingend 400 of the BIC 50. Like apertures 8, 9, cavities 11, 12 areapproximately 2 inches long and 0.5 inch wide. In addition, cavity 11 ispreferably spaced approximately 3 inches from the left lateral side 225of the BIC 50 and cavity 12 is set approximately 3 inches from the rightlateral side 226 of the BIC 50.

Referring now to FIG. 22, in the automated system structured accordingto the principles of the present invention, it is necessary to utilizesome type of automated carrier means to transport the BIC 50. Thecarrier means or shuttle apparatus 210 disclosed herein includes twoinverted T-shaped handles 83, 84 which are used to grasp the BIC 50thereby permitting automatic handling of the BIC 50. The invertedT-shaped handles 83, 84 have a connecting rod 286, forming the verticalpart of the inverted "T", and a horizontal base part 189 positioned atthe bottom of the connecting rod 286. The connecting rod is attached tothe horizontal base part 189 in such a manner as to divide thehorizontal base part into two equal end portions 88, 89. Connecting rod286 extends from and retracts into the carrier means to extend and toretract base part 189. End portions 88, 89 are each approximately 0.75inch in length. The diameter of end portions 88, 89 tapers from about0.625 inch at the connecting rod 286 down to 0.375 inch at the endpoint.

To grasp the cartridge, the two inverted T-shaped handles 83, 84 areextended from the carrier means and inserted into cavities 11, 12 set inthe grasping end 400 of the BIC 50. The T-shaped handles 83, 84 areinserted until they are inline with apertures 8, 9 and then are rotated90 degrees. Rotation of the T-shaped handles 83, 84 causes the endportions 88, 89 of each T-shaped handle 83, 84 to protrude fromapertures 8, 9. End portions 88, 89 bind securely in apertures 8, 9 dueto their tapered diameter; consequently when the T-shaped handles 83, 84are retracted by the retraction of connecting rod 286 back into thecarrier means, the BIC 50 is also retracted.

A bar code label 55 may be provided in a convenient location on eachside face 56 of the BIC 50 to identify the particular side face and theparticular cartridge in the automated burn-in system (FIG. 15).Alternatively, an electrical code may be used which includes anarrangement of circuit elements on the burn-in board cartridge, such asdiodes, which can be scanned by inputting and outputting an electricalsignal. The bar code label identifies both the tube and IC packages inthe tube.

A plurality of T-shaped handle pairs 83, 84 may be provided to permitthe simultaneous or almost simultaneous loading and unloading of aplurality of cartridges. In the preferred embodiment, the shuttleapparatus 210 is capable of carrying "n" number of cartridges, where "n"is equal to the number of slots in each electrical zone of a burn-inchamber. Similarly, "n" number of T-shaped handle pairs 83, 84 arepreferably provided in the shuttle apparatus 210, so that there is onehandle pair for each cartridge 50. As a result, an entire burn-inchamber zone can be loaded at one time. After the shuttle is positionedbeside or above the burn-in chamber, the cartridges are preferablyplaced in the chamber simultaneously. Each of the cartridges is theninserted into the connectors 25 in a sequential fashion, one afteranother, in the manner described above, in order to minimize the totalforce exerted by the shuttle apparatus on the chamber at any one time.

The BIC 50 may also comprise a single-sided burn-in board. Referring nowto FIGS. 15, 18, and 23, the single-side cartridge, like the two-sidedcartridge, includes frames 21, 22, cross beams 31, connectors 25,sockets 38, rails 28, 29, apertures 8, 9 and cavities 11, 12. Thesingle-sided cartridge, however, uses only one printed circuit card 30.The grasping end 400 of the single-sided cartridge includes graspingsupport 450 which is used to insure stability of the single printedcircuit card. The grasping support 450, shown in FIG. 23, has atruncated pentagonal configuration which in cross-section resembles ajar with a bottle-neck. The single printed circuit card 30 is placed inthe opening of the grasping support 450. The sides of the U-shapedcartridge frames 21, 22 are also partially within the support 450, withthe outer sides of the frames 21, 22 extending therefrom. As a result ofthis construction, the printed circuit card 30 is sandwiched at itsgrasping end between the grasping support 450 and the front side offrames 21, 22. A screw, bolt, rivet, or other suitable fastening means105 is used to hold the circuit card between the support 450 and theframes 21, 22. The other open side of the grasping support 450 issecured to the back side of frames 21, 22.

The grasping support includes apertures 8, 9 and cavities 11, 12 topermit automatic handling of the single-sided cartridge by the shuttleapparatus 210 in a manner similar to the two-sided cartridge.

The burn-in board cartridge 50 presents a myriad of advantages over theconventional burn-in board. Frames 21, 22 provide a sturdy structure andprevent circuit cards 30 from warping or being damaged. In addition, thecross-beams 31 provide added stability to frames 21, 22 and reduce theamount of flexing that occurs at the printed circuit card whenever ICpackages are inserted into or removed from the BIC 50. Since oneconfiguration of BIC 50 is two-sided, electronic circuitry 281 can beplaced between the printed circuit cards in a position close to thesockets as preferred in high speed digital circuits (see FIG. 20). Inthe single-sided cartridge, electronic circuitry 281 can be placed onthe back of the printed circuit card. Blowing nitrogen or cool ambientair through tube 46 into the end interior chamber 43a of the two-sidedBIC serves to maintain test circuitry at lower temperatures, therebysubstantially extending the life of the circuitry.

Furthermore, the two-sided configuration of BIC 50 is capable ofhandling certain IC packages which cannot be handled by conventionalburn-in boards due to the great number of leads possessed by the ICpackage. The great number of leads requires more input and outputconnections than are available on the edge connector of a conventionalburn-in board. The two sided configuration of burn-in cartridge 50 makesburn-in and testing of these packages possible by utilizing connectorsfrom both side faces of the two-sided BIC 50. Referring now to FIG. 21,an end printed circuit card 501 is provided at the grasping end 400 ofthe two-sided configuration BIC 50 and is connected electrically to theprinted circuit cards placed on each side face of the BIC 50 so that thetwo sides of the BIC literally comprise one printed circuit card. Sincethe two-sided BIC has twice as many edge connections as a conventionalburn-in board, one edge connector can be used for input connections andthe other can be used for output connections. For example, one side ofthe BIC could be used solely to receive input signals while the otherside of the BIC could be used solely to deliver output signals.

III. BURN-IN CHAMBER

Referring now to FIGS. 24, 26 and 27, a burn-in chamber 160 constructedin accordance with the principles of the present invention includes aninstrumentation housing 170, a power supply housing 175, a mother boardcabinet (201), and one or more stress chambers 155. Except as otherwiseset forth herein, the burn-in chamber 160 is constructed and operates insubstantially the same manner as a conventional burn-in chamber such asis well-known to those skilled in the art. Thus, the instrumentationhousing 170 includes a microprocessor for coordinating the burn-in andtest process for the stress chambers, as well as the various apparatusnecessary to control the thermal environment of the stress chambers 155.The power supply housing 175 includes the various apparatus necessary tosupply and to control the supply of electrical power to the burn-inboards and electronic apparatus connected thereto. In addition,equipment in the power supply housing may supply power to theinstrumentation equipment and may receive control signals from themicroprocessor. The mother board cabinet 201 encloses the variousprinted circuit boards 127 on the exterior backplane of the stresschambers 155. These boards 127 include mother boards, into which theburn-in cartridges are plugged, clocking boards for generating theelectrical signals that exercise the IC packages on the burn-incartridges, and monitor boards, which monitor the burn-in cartridges forthe presence of clocking signals.

The burn-in chamber 160 may also include a test cabinet 165 for housingthe electronic apparatus necessary to conduct functional testing of ICpackages within the stress chambers 155.

Referring still to FIG. 24, the stress chambers 155 (two of which aredepicted in FIG. 24) are surrounded on all sides by an exterior wall147, which is preferably formed of a steel interior and exterior with amiddle of fiberglass (or marinite) 159 to insulate the stress chambers155 from other portions of the burn-in chamber 160. A mid-chamber wall145, constructed in substantially the same manner as the exterior wall147, divides each stress chamber into left and right sections 252,254.The mid-chamber wall 145 extends through the entire horizontal depth ofthe stress chamber with the top of the wall spaced vertically below thetop of the stress chamber so as to form an upper duct 246, and thebottom of the wall spaced vertically above the bottom of the stresschamber so as to form a lower duct 248. Each stress chamber alsoincludes a heater mechanism 153, of a type well-known in the art, forheating the interior of the stress chamber and an air mover mechanism157, also of a type well-known in the art, for circulating air throughthe stress chamber so as to maintain a minimal temperature gradientthroughout the chamber. While air is the preferred medium used in thestress chamber 155, nitrogen, an air/nitrogen mixture, or fluorinatedfluid may also be used in the burn-in process. In operation, the airmover 157 forces air downwardly through right section 254, horizontallythrough lower duct 248, and then upwardly through left section 252 ofthe stress chamber. Preferably, air mover 157 should drive the air at arate of approximately 30 feet per second in order to maintain a narrowtemperature gradient during the burn-in process.

In a burn-in chamber 160 constructed in accordance with the principlesof the present invention, each stress chamber is divided into aplurality of burn-in zones 260. Each burn-in zone 260 supports aplurality of burn-in cartridges and can be operated substantiallyindependently of other zones 260. Thus, each zone 260 is electricallyindependent of every other zone, whereby clocking signals communicatedto burn-in cartridges may be varied from zone to zone. In addition, eachzone 260 may be isolated thermally from all other zones, whereby burn-incycle timing may vary from zone to zone. The number of zones 260 in eachstress chamber 155 may vary according to the desired capacity of thestress chamber.

Each zone 260 comprises a plurality of cartridge support structures 61,one for each burn-in cartridge in the zone 260, a connection deviceassembly 122, an opening for providing access to the zone 260, and anair diverter mechanism 125. Each cartridge support structure preferablycomprises the structures 61 depicted in FIG. 20, and described in detailsupra in the section entitled "Burn-in Cartridge." The structures 61 arepositioned adjacent to one another and are spaced one from the next toaccomodate the flow of air between cartridges received therein. Thenumber of burn-in cartridges supported by each zone 260 may varyaccording to the demands of each burn-in system, but preferablycomprises four to eight cartridges.

The connection device assembly 122 is the electrical connectionapparatus by which electrical signals are communicated to and receivedfrom the burn-in cartridges. The connection device assembly of thepresent invention preferably is constructed in the manner disclosed inU.S. Pat. Nos. 4,374,317 and 4,507,544, which are expressly incorporatedherein by reference, with the assembly forming a part of the rear wallof the stress chamber. As described in detail in the named patents, edgeconnections on the burn-in cartridges are received through slots 270 (inFIG. 24) in the rear wall of the zone 260 into edge connectors forming apart of a mother board. Clocking boards and monitor boards, which areconnected electrically to the opposing face of the mother board by meansof edge connectors, generate the electrical signals necessary toexercise and monitor the particular type of IC packages supported on thecorresponding burn-in cartridges, in a manner now well-known to thoseskilled in the art. The connection device assembly also preferablyincludes as a part of the rear wall of the stress chamber the isolationapparatus described in detail in U.S. Pat. No. 4,374,317.

The opening in the front portion of each zone 260 permits access to thezone. Each opening is covered by an associated door 172, such that whenthe door 172 is closed, the associated zone is substantially thermallyinsulated from the ambient outside the zone Each door 172 is constructedin such a manner as to enable it to be opened and closed automaticallyfor insertion and removal of burn-in cartridges.

The air diverter mechanism 125 is an apparatus that controls the flow ofhot air moving through the stress chamber, whereby hot air may bediverted around the outside of a zone in order to insert or removeburn-in cartridges from the zone while burn-in progresses in adjacentzones. The air diverter mechanism comprises a pair of zone sidewalls91,93 extending alongside each zone and a pair of rotatable baffles250,251 positioned at the upstream end of each zone.

The zone sidewalls 91,93 preferably comprise insulated steel platesapproximately one inch thick positioned on opposing sides of each zone.The sidewalls, which extend horizontally through the full depth of thezone, are generally parallel to and spaced from the adjacent mid-chamberwall 145 or exterior wall 147, whichever is applicable, of the stresschamber 155 to define dual airflow paths 95,97 around the outside of thezone. The vertical dimension of the sidewalls 91,93, and hence theairflow paths, is approximately the same as that of the correspondingzone. In order to maintain approximately the same cross-sectional areafor airflow through the zone 260 and the alternative airflow paths95,97, the sidewalls 91,93 preferably are spaced from the correspondingmid-chamber or exterior wall by approximately one-half of the distancebetween the two zone sidewalls.

Referring to FIGS. 24 and 25A-C, the baffles 250,251 are comprised ofthree steel blades 113,115,117 mounted in parallel between a frontoblong endplate 177 and a rear oblong endplate 179 and thus extend fromthe rear wall of the stress chamber 155 to the front wall of the stresschamber.

Each baffle rotates on a shaft 163 that extends from abearing-engagement in the front wall of the stress chamber through thefront endplate 177, lengthwise through the center of the middle blade115, through the rear endplate 179, through a bearing-engagement in therear wall of the stress chamber, and into the mother board cabinet,where it connects with a baffle drive mechanism 215, as described below.The shaft 163 for each baffle is positioned above and in alignment withthe corresponding zone sidewall, whereby the middle blade can be rotatedinto metal-to-metal substantially sealing engagement with the upper endof the sidewall when the middle blade 115 is substantially aligned withthe sidewall, as depicted in FIG. 25C.

The middle blade 115 preferably defines an aerodynamic profile taperedto a point along the lengthwise edges so as to minimize turbulence inthe airflow through the stress chamber. If the baffle is positionedbeneath an adjacent zone, the shaft 163 is positioned halfway betweenthe upper end of the first zone sidewall and the lower end of theadjacent zone sidewall, whereby the middle blade 115 can be aligned toform a sealed extension between the two sidewalls 91,93, as shown inFIG. 25C.

Each pair of baffles 250,251 has associated therewith a baffle supportrod 194, approximately one inch in diameter, which extends horizontallythrough the stress chamber at the same horizontal level as and halfwaybetween the shafts 163 of the associated pair of baffles 250,251.

Collateral blades 113,117, positioned on opposing sides of and generallyparallel to the middle blade 115, are generally plate-shaped withrounded lengthwise edges so as to facilitate airflow through the stresschamber 155 with minimal turbulence. Outer collateral blade 113 iswelded to the outer side of the front and back oblong endplates, whileinner collateral blade 117 is welded to the interior side of the twoendplates.

The blades 113, 117 are of such a width that when the downstream end ofthe baffles 250,251 are rotated toward one another, as in FIG. 25B,outer blade 113 effectively caps the downwind air path by forming a sealbetween the downwind zone's outer sidewall and either the chamber wallor mid-chamber wall. At the same time, the inner blades 117 converge atthe downwind edges to form a "V", with the upstream edges of innerblades 117 sealingly engaging the upwind zone sidewalls 91,93, and thedownwind edges sealingly engaging the support rod 194.

When the downstream end of the baffles rotate outward, as in FIG. 25A,inner blades 117 form an inverted "V", capping the downstream zone 260.The downstream edges of the innner blades 117 sealingly engage thedownstream zone sidewalls, while the upstream edges sealingly engage thesupport rod 194. The outer blades 113 sealingly engage the downstreamedge of the upstream sidewall and either the chamber wall or mid-chamberwall, whichever is applicable.

Referring to FIGS. 26 and 27, baffle drive mechanism 215 comprises astepping motor 220 and coupling gears 205. Stepping motor 220 preferablycouples directly to one shaft 163a of the baffle pair 250,251. Couplinggears 205 comprise a pair of gears 320,322, which couple themotor-driven shaft 163a to the second shaft 163b in a one-to-one ratio,whereby the two shafts rotate in opposite directions by the same angulardisplacement at all times.

Preferably, the baffle drive mechanism 215 attaches to shafts 163a,163bon the rearward side of mother board cabinet 201 so as to avoid anycontamination of electronics within the mother board cabinet 201.Alternatively, however, the drive mechanism 215 may be included withinthe interior of the mother board cabinet 201, in the available spacebetween the clock/monitor boards 127 for each burn-in zone. In thealternative embodiment, the drive mechanism 215 preferably is itselfenclosed by a partition to prevent contamination of the electronicswithin the cabinet 201.

In operation, the microprocessor within the instrumentation cabinet 170communicates commands to a motor controller (not shown) for the steppingmotor 220. In response to these signals, stepping motor 220 rotatesshaft 163a a predetermined angular distance in either a clockwise orcounterclockwise direction. Angular motion of shaft 163a is translatedby coupling gears 205 into angular motion of shaft 163b in the oppositedirection, thereby effecting movement of the corresponding pair ofbaffles 250,251 to the desired position.

Referring to FIGS. 25A-C, the operation of the air diverter mechanismwill be discussed. The baffles 250,251 channel the air driven by the airmover 157 through and around the zones of the stress chamber 155.Normally, the baffles 250, 251 are maintained in the neutral positiondepicted in FIG. 25C to d41irect the flow of air through the downstreamzone 260 and prevent the flow of air within the airflow paths 95, 97. Byrotating the downstream ends of the pair of baffles 250,251 away fromone another, as shown in FIG. 25A, the hot air is diverted around thedownstream zone 260 and through airflow paths 95,97 around the outsideof the zone. The airflow can be re-channeled from the air paths 95,97back through the next downstream zones 260 by rotating the downstreamends of the intervening baffles toward one another, as shown in FIG.25B.

The ability to bypass a zone by channeling hot air around the zoneprovides many advantages not present in prior art burn-in chambers. Eachburn-in zone may operate, in effect, as a separate burn-in chamber,being subjected to burn-in or being cooled down, as desired. Inaddition, since a separate chamber door 172 is provided for each zone260, cooling can be accelerated in any one zone by bypassing the zoneand then opening the associated door.

Burn-in zones can also be loaded and unloaded individually once cooled,while burn-in continues in other zones. As a result, overall IC packagethroughput can be maximized by loading and unloading each individualzone as burn-in is completed.

As described herein, the preferred embodiment of the burn-in chamber 160comprises a horizontal stress chamber, in which the door to each burn-inzone is positioned on one side of the stress chamber whereby burn-incartridges move generally horizontally into and out of the stresschamber. In an alternative embodiment of the present invention, such asis depicted generally in FIG. 2, the burn-in chamber 160 comprises avertical stress chamber wherein the zone doors are located on the top ofthe stress chamber, and burn-in cartridges are moved generallyvertically into and out of the stress chamber. The vertical stresschamber, which is essential for liquid burn-in techniques andparticularly useful for conservation of floor space, is constructedaccording to the same basic principles set forth herein, except perhapsfor positioning of the instrumentation and power supply cabinets, whichmay preferably be located beneath rather than beside the stress chamber.

IV. AUTOMATIC HANDLER

FIGS. 28-30 depict certain details of the automated handler 275, whichwas described generally supra in the section entitled, "Burn-inCartridge." In the preferred embodiment, the shuttle apparatus 210 (FIG.22) includes a pair of automated handlers for grasping each burn-inboard cartridge 50. This discussion focuses on a single automatedhandler, it being understood that a number of identical automatedhandlers may be constructed accordingly and used with the shuttleapparatus 210 shown in FIG. 22, as described in more detail hereafter.

Referring now to FIGS. 28 and 29, the automated handler 275 preferablyincludes a support block 290, an outer shaft 217, an inner shaft 283, anangular displacement mechanism 258, and a linear displacement mechanism272. The outer shaft 217 is threadedly engaged within the support block290 and threadedly engages the inner shaft 283, which extends generallycoaxially through the outer shaft 217 and through the support block 290.One end of the inner shaft 283 is arranged to engage a BIC 50, and theother end of the inner shaft interacts cooperatively with the angulardisplacement mechanism 258. The angular displacement mechanism 258, asdiscussed herein, causes the handler 275 to rotate through an arc ofapproximately 90 degrees whereby the inner shaft 283 engages ordisengages the BIC. The linear displacement mechanism 272, with which aportion of the support block 290 interacts, as hereinafter described,causes limited vertical displacement of the engaged BIC, wherebyconnector edges on the BIC may be inserted within or removed from one ormore edge connectors.

More particularly, the support block 290 comprises a support housing 212having a generally rectangular cross section, a central bore 204machined within the housing 212, and a slotted lip 99, which protrudesfrom one face of the housing 212 and which interacts cooperatively withthe linear displacement mechanism.

Referring still to FIGS. 28 and 29, support housing 212 includes sixfaces, hereinafter described as a front face 129, a back face 124, aleft face 192, a right face 193, a top face 128 and a bottom face 232.Central bore 204, which may vary in diameter as reflected generally inFIG. 28, extends through support housing 212 from the right face 193 tothe left face 192. A portion of the interior surface of the central bore204, that intersects the right face 193 of support housing 212, ismachined to form female threads for receiving the outer shaft 217.

Slotted lip 99 includes a cam support body 197 having a cam groove 188machined therein. The cam support body 197 comprises a solid protrusionof generally rectangular cross section, as viewed in FIG. 29, machinedin the top face 128 of the support housing 212. The cam groove 188comprises a linear groove of generally rectangular cross sectionmachined in the portion of the top face 128 formed by cam support body197. The centerline of the cam groove 188 is angled with respect to theplanes defined by the left and right faces 192, 193 of the supporthousing 212, whereby walls 292, 293 of the groove 188 form bearingsurfaces for receiving a roller bearing 151 forming a part of the lineardisplacement mechanism. Motion of the roller bearing within the groove188 along a line generally parallel with the plane of the left andrights faces 192, 193 is thereby translated to axial displacement of thesupport block 290. The dimensions of the same support body 197 and thecam groove 188 are calculated according to known engineering principlesso as to enable the slotted lip 99 to support insertion and removal of aconnector edge on a BIC into and out of a card edge connector.

Referring still to FIG. 28, the outer shaft 217 comprises a bushing 294threadedly engaged within the support block 290 and a locknut 297.Bushing 294 includes a stem 282 bearing male threads for engaging thethreaded portion of the interior surface of the central bore 204, ahexagonally-shaped cap 277, and a vertical bore 211 extending throughthe stem 282 and cap 277 and defining a hollow interior surface in theouter shaft 217. Threaded stem 282 is machined to include femalethreads, preferably of the acme-type, on the hollow interior surface ofthe stem 282, as well as the above-mentioned threads on the exterior ofthe stem 282. Cap 277 is fixedly attached to the upper end of threadedstem 282, whereby the axial displacement of the stem 282 within thesupport housing 212 may be adjusted by rotation thereof.

Locknut 297 is a hexagonally-shaped nut that threadedly engages theexterior surface of the threaded stem 282 between the support housing212 and the bushing cap 277. Tightening locknut 297 against the rightface 193 of support housing 212 secures the outer shaft 217 in a fixedposition relative to the support housing 212. Loosening locknut 297enables bushing 294 to be inserted further into or removed from thecentral bore 204 of the support housing 212.

The inner shaft 283 comprises a generally cylindrical rod 286 having atone end a handle 83 for engaging a BIC 50 and at the other end a camlever 107 for cooperative interaction with the angular displacementmechanism 258. More particularly, the rod 286 has a first end 121forming a part of the handle 83, a middle portion 119 extending throughthe central bore 204 of the support housing 212 and the vertical bore211 of the outer shaft 217, and a second end 123 forming a part of thecam lever 107. The middle portion 119 of connecting rod 286 is machinedto define a male thread, preferably of the acme-type, for engagementwithin the outer shaft 217, whereby the axial displacement of the innershaft 283 relative to the support block 290 may be adjusted easily.

As described supra in Section II, entitled "Burn-in Cartridge," handle83 may have an inverted T-shaped configuration. In the preferredembodiment of FIG. 28, handle 83 comprises a cross-bar 191 extendinggenerally perpendicularly through the rod 286 approximately one inchfrom the end 121 of the rod 286. The cross-bar 191 may be, for example,a generally cylindrical rod received within a bore in the rod 286 andattached therein whereby two equal end portions 288, 289 with a lengthof approximately 0.75 inches extend from opposing sides of the rod 286.The diameter of end portions 288, 289 preferably taper fromapproximately 0.625 inch near the rod 286 to approximately 0.375 inchnear the outer ends thereof.

Referring now to FIGS. 28 and 29, cam lever 107 comprises a lever body111 supporting a pair of spaced cam fingers 242, 244. The lever body 111is secured to the second end 123 of the rod 286, with cam fingers 242,244 extending generally perpendicularly of the axis of the rod 286. Camfingers 242, 244, as shown in FIG. 29, form an elongated U-shapedconfiguration, defining therebetween a cam slot 103. The side walls ofcam slot 103 comprises bearing surfaces that will accommodate a rollerbearing 161 forming a part of the angular displacement mechanism 258,whereby linear motion of the roller bearing 161 will engage the cam slot103 and cause the rod 286 to rotate through an arc of approximately 90°.

Referring still to FIGS. 28 and 29, the angular displacement mechanism258 constructed in accordance with the principles of the presentinvention comprises a cam roller bearing 161, which engages and rotatescam lever 107, a bearing support apparatus 209, and a ball screw 109coupled to a motor (not shown).

Bearing support apparatus 209 comprises a central post 167 rotatablysupporting the cam roller bearing and a pair of spaced, horizontallyextending bearing support arms 202, 203 attached to each end of thecentral post 167, and a cam support block 118. The roller bearing 161preferably has an axial length of approximately two inches and adiameter that is slightly less than the width of cam slot 103 betweencam fingers 242, 244. Central post 167 extends axially along the lengthof the roller bearing 161. Post 167 has a length that is greater thanbearing 161 so that the top and bottom ends of post 167 protrude beyondthe ends of bearing 161. Cam arms 202, 203 connect to the top and bottomends of central post 167 and extend perpendicularly therefrom.

The cam support block 118 comprises means for supporting cam arms 202,203 and a threaded bore 206 for receiving therethrough the ball screw109, whereby the roller bearing 161 may be moved along a line so as toeffect angular motion sequentially to a plurality of cam levers 107.Thus, cam arms 202, 203 are secured to the cam support block 118 tosupport the roller bearing 161 therefrom. The threaded bore extendsthrough the cam support block 118 along a line generally perpendicularto the plane of the support arms 202, 203.

Referring now to FIGS. 22 and 28, in the preferred embodiment, ballscrew 109 extends generally horizontally through the interior of theshuttle apparatus 210, adjacent to the cam lever 107 of each handler275, in a direction transverse to cam arms 202, 203. Ball screw 109threadedly engages the threaded bore of threaded block 118 so that thethreaded block 118 traverses along ball screw 109 as ball screw 109 isturned in a conventional manner by, for example, a stepper or othersuitable motor directly coupled to the ball screw 109. As threaded block118 moves horizontally, vertical cam follower 209 engages cam lever 107and rotates lever 107 approximately 90 degrees, thereby rotating innershaft 283 and handle 83 ninety degrees to engage and disengage BIC 50.

Referring now to FIGS. 28 and 29, the linear displacement mechanism 272constructed in accordance with the preferred embodiment comprises a campin roller bearing 151, which engages the cam groove 188 in the slottedlip 99 in support block 290, a bearing support apparatus 221, and a ballscrew 219 coupled to a motor (not shown) in a conventional manner. Byengaging the cam groove 188, the pin roller bearing 151 thereby linearlydisplaces support block 290, outer shaft 217 and inner shaft 283,whereby handler 275 may move the BIC 50 so as to cause the BIC 50 to beconnected and disconnected from connectors 25 (shown in FIG. 19).

The bearing support apparatus 221 comprises a central post 152 rotatablysupporting the pin roller bearing 151 and a cam support block 223.Bearing 151 includes an engaging end 169 that may be received in the camgroove 181; has an axial length preferably in excess of the depth of thecam groove 181 in the support housing 212; and has a diameter that isslightly less than the cam groove 188. Central post 152, with a lengthgreater than that of bearing 151, extends axially through the bearing151 and lies flush with the engaging end 169 of bearing 151. Post 152protrudes from the end of bearing 151 opposite the engaging end 169 andconnects permanently to the cam support block 223.

The cam support block 223 includes a threaded bore that extends throughblock 223 perpendicularly of central post 152.

In a construction similar to that of ball screw 109, ball screw 219extends generally horizontally across the interior of the shuttleapparatus 210 in a direction transverse to central post 152 and cam arms202, 203. Ball screw 219 threadedly engages the threaded bore of camsupport block 223 in such a manner that cam support block 223 moveshorizontally along ball screw 219 as ball screw 219 is rotated by adirect-coupled motor. As cam support block 219 moves horizontally, pinroller bearing 151 also moves horizontally and engages cam groove 181.As the pin roller bearing 151 moves generally horizontally along a linedefined by ball screw 219, it traverses the cam groove 188. Motion ofthe bearing through the cam groove is translated by the angular extentof the cam groove 188 to axial displacement of the handler 275, thedirection of displacement being dependent upon the angle of the grooveaxis relative to the planes of left and right faces 192, 193 of thesupport housing 212. Axial motion of the handler 275 connects anddisconnects BIC 50 into and out of its associated edge connector.

According to the preferred embodiment, as described supra in section II,entitled "Burn-in Cartridge," a plurality of handler pairs may beprovided to permit the handling of a plurality of BICs 50. Thus, aplurality of automated handler pairs may be provided to engage andinsert BICs 50 automatically in a sequential fashion.

According to the preferred embodiment as further described herein, twoparallel rows of automated handlers, each with "n" number of handlers,define "n" pairs of automated handlers, each pair being capable ofattachment to a single BIC 50. The discussion herein focuses on theoperation of a single such row of automated handlers, it beingunderstood that the second row would be constructed identically.

Referring now to FIGS. 28 and 30, and generally to the angulardisplacement mechanism 258 described supra, a plurality of automatedhandlers 275 are positioned sequentially along a single line, or row.Ball screws 109 and 219 extend generally horizontally along beside therow of handlers 275. In the preferred embodiment, as shown generally inFIG. 28, the length of the inner shaft 283 alternates between twodifferent lengths, whereby every other handler 275 has an inner shaft283 of a same length. The difference in length of adjacent inner shafts283 is less than the axial length of cam roller bearing 161, whereby camroller bearing 161 can engage the cam lever 107 on adjacent handlers 275sequentially. Thus, the cam levers 107 for the row of handlers 275define a pair of spaced, parallel planes. The alternate positioning ofcam levers 107 enables adjacent handlers 275 to be positioned moreclosely to one another than would otherwise be possible given therequired angular motion of cam lever 107.

Referring now to FIG. 30, as the cam roller bearing 151 moves generallyhorizontally in response to rotation of ball screw 109, it engages thefirst cam lever 107 in the row of handlers and rotates it approximately90 degrees before disengaging the first cam slot 103. As cam rollerbearing 161 disengages the first cam lever 107, it immediately engagesthe second cam lever 108, with cam finger 244 of the first cam lever107, overlapping cam finger 342 of the second cam lever 108, asdescribed supra. As vertical cam follower 209 traverses the length ofball screw 109, each cam lever 107, 108 is sequentially engaged androtated 90 degrees to cause each handle 83 to engage (or disengage)sequentially a BIC 50.

Referring now to FIGS. 28 and 30, and generally to the lineardisplacement mechanism 272 described supra, the support blocks 290 ofadjacent handlers 275 are aligned one to the next such that the cam pinroller bearing 151 moving generally horizontally along a path defined bythe ball screw 219 will engage the cam groove 188 in the slotted lip 99on each support block 290. As the cam pin roller bearing 151 movesgenerally horizontally, it engages an edge of the cam groove 188 on thefirst handler 275. As the roller bearing continues to move generallyhorizontally, the angular orientation of the cam groove 188 relative tothe ball screw 219 causes the support block 290 to be displaced axially.Immediately after exiting from the first cam groove 188, the cam pinroller bearing 151 engages the cam groove on an adjacent support block290, axially displacing the second handler 275 in the same manner as thefirst. In this manner, each handler 275 is displaced sequentially toconnect or disconnect each BIC 50 sequentially so as to minimize thetotal force required to be exerted by the shuttle apparatus on thechamber at any one time, as discussed supra, in section II.

According to the preferred embodiment of the invention, the automatedhandlers may be oriented for motion either vertically or horizontally,depending upon the configuration of the chamber being serviced thereby,without departing from the description set forth herein. While apreferred embodiment of the invention has been shown and described,modifications can be made by one skilled in the art without departingfrom the spirit of the invention.

What is claimed is:
 1. Apparatus for automatically inserting andremoving a burn-in board in a chamber, said burn-in board being used forburning-in integrated circuits, comprising:means for grasping theburn-in board; means connected to said grasping means, for displacingsaid grasping means angularly to lock said grasping means onto theburn-in board; and means for displacing said grasping means linearly toinsert the burn-in board into and remove the burn-in board from aconnector in said chamber.
 2. Apparatus according to claim 1 whereinsaid grasping means includes a handle and a cylindrical rod attached tothe handle.
 3. Apparatus according to claim 2 further comprising abushing disposed about a portion of said rod for adjusting thepositioning of said handle.
 4. Apparatus according to claim 3, whereinsaid linear displacement means is disposed about said rod.
 5. Apparatusaccording to claim 4, further comprising a bushing disposed between saidrod and said linear displacement means.
 6. Apparatus according to claim5 wherein said bushing includes a bushing head and a hollow body portionwith an interior surface and an exterior surface;the interior surface ofthe hollow body portion is threaded; a portion of said rod is threaded;and said rod is screwed into the hollow body portion of said bushing andmates with the threaded interior surface of the hollow body portion. 7.Apparatus according to claim 6 further comprising a block portiondisposed between said bushing and said linear displacement means. 8.Apparatus according to claim 7 wherein a bore is machined into saidblock portion;part of said bore is threaded; the exterior surface of thehollow body portion of said bushing is threaded; and the hollow bodyportion of said bushing is screwed into said bore.
 9. Apparatusaccording to claim 5 further comprising a block portion disposed betweensaid bushing and said linear displacement means.
 10. An automatichandler according to claim 4 further comprising a rectangular blockportion, with a front and a back, disposed about said rod, and saidlinear displacement means includes a slot in said block portion whichextends along one side of said block portion from the front of saidblock portion to the back of said block portion.
 11. An automatichandler according to claim 10 wherein said slot angles downwardly fromthe front to the back of said block portion.
 12. An automatic handleraccording to claim 11 wherein said linear displacement means includes aroller bearing movable about a fixed axis, with a portion of said rollerbearing received within said slot as said roller bearing moves along theaxis.
 13. An automatic handler according to claim 12 wherein said lineardisplacement means includes a ball screw, positioned in a plane parallelto the fixed axis, a threaded block, disposed about the ball screw, andsaid roller bearing connects to the threaded block.
 14. An automatichandler according to claim 10 wherein said slot is angled from the frontto the back of said block portion.
 15. Apparatus according to claim 2wherein said angular displacement means includes a cam lever connectedto said rod and a roller bearing movable about a fixed axis, with theroller bearing engaging the cam lever as the roller bearing moves aboutthe axis.
 16. An automatic handler according to claim 15 wherein saidangular displacement means includes a ball screw positioned in a planeparallel to the fixed axis, a threaded block connected to the rollerbearing, and the threaded block being disposed about the ball screw. 17.Apparatus according to claim 1 wherein said grasping means includes aT-shaped handle.
 18. Apparatus for handling a plurality of burn-inboards, each burn-in board having a connector edge that may be receivedwithin one of a plurality of edge connectors comprising:a plurality ofmeans for grasping a burn-in board, at least one said grasping meansprovided for each burn-in board of the plurality of burn-in boards;means for displacing each of said grasping means angularly to connectand disconnect said grasping means to and from the burn-in boards; andmeans for displacing each of said grasping means linearly to connect anddisconnect the burn-in boards to and from edge connectors.
 19. Apparatusaccording to claim 18, wherein said linear displacing means engages saidplurality of grasping means sequentially, one of said grasping means ata time, to insert and remove each burn-in board of the plurality ofburn-in boards from the edge connector so as to limit the total forceapplied to the plurality of edge connectors at any one time. 20.Apparatus according to claim 18, wherein said angular displacing meansengages said plurality of grasping means sequentially, one said graspingmeans at a time, to connect and disconnect each grasping means to andfrom the burn-in boards so as to limit the total force required at anyone time to effect the connection and disconnection.
 21. An automatichandler comprising:a plurality of grasping means aligned in a row; aplurality of cylindrical rods aligned in a row, each of said pluralityof cylindrical rods including a first and second end; a plurality of camlevers; each of said handling means connected to the first end of one ofsaid rods, and each of said cam levers attached to the second end ofsaid rods; a roller bearing, movable along a fixed axis, engaging eachof said plurality of cam levers and rotating each said cam lever as saidroller bearing moves along the axis.